[Docs]: Add example to motion slot Loop docs

[robertpenner]

Area

React Components (https://react.fluentui.dev)

What kind of documentation issue are you reporting?

• Reporting a typo
• Reporting a documentation bug
• Documentation improvement
• Documentation feedback

Is there a specific documentation page you are reporting?

https://microsoft.sharepoint.com/:fl:/s/f2392a25-7d22-4e39-acba-97ad7368c90a/EZrUvXcDyw5Jlcud0LrYRmUBbJp63fl55QUYYIyzGenkaw?e=pkH9IK&nav=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

Description

Expand motion slot documentation with a concrete example, e.g. how to customize Accordion via motion slot.

Validations

• Check that there isn't already an issue that requests the same feature to avoid creating a duplicate.